Study on guanidino-carboxylate interactions in copper(II) ternary complexes of guanidinoacetic acid with glutamic and aspartic acids

The possibility of occurrence of biological relevant guanidino-carboxylate interactions was investigated in ternary systems involving guanidinoacetic (Gaa) and glutamic acid (Glu), aspartic acid (Asp) or glycine (Gly). The study was done in solution using potentiometry, ultraviolet visible and EPR spectroscopy. The stability constants of the ternary complexes as well as the binary ones were potentiometrically determined (T = 25 degreesC, mu = 0.1 mol 1(-1), KNO3). The order of the stability constants of ternary complexes was CuAspGaa > CuGluGaa > CuGlyGaa. Deltalog K(log beta CuLGaa - (log beta CuL + log beta CuGaa) L = Glu, Asp or Gly) showed that Asp and Glu favored more stable ternary complexes while Gly formed a less stable ternary complex than its binary ones. Comparison between statistical and experimental log beta CuLGaa suggested guanidino-carboxylate interactions in CuAspGaa and CuGluGaa, involving the guanidino group from Gaa and the non-coordinated-carboxylate group from Glu or Asp, possibly through hydrogen bonds. (C) 2002 Elsevier Science Ltd. All rights reserved.